The invention relates to a hydraulic fluid pressure operated control mechanism for use in hydraulic systems for their controlling, more specifically for use in hydraulic systems for hydrostatic transmissions comprising a variable displacement pump and a variable displacement motor.
Because of limited assembling space it is important to have hydrostatic transmissions which are compact in design. From that results that the displacement adjusting systems for such hydrostatic transmissions have to be small and therefore must be supplied with system pressure to guarantee the secure change of displacement under all operating conditions.
A disadvantage of such displacement adjusting systems is that long adjusting times, which are desirable for reducing jerkiness in vehicles having hydrostatic transmissions, are only realized with very small orifices. Unfortunately, very small orifices are susceptible to blockage by fluid-borne contaminants. It is usually important for the driving performance of a vehicle that the response time from minimum displacement to maximum displacement be different depending on whether the vehicle is moved in a forward or reverse direction. Therefore, it is desirable to have a different size orifice for each direction. Another difficulty can arise when the driver, at high driving speed, attempts to set the variable displacement motor at a large swashplate angle and the rapidly increased displacement of the motor cannot be delivered by the pump. The consequence can be an extremely abrupt deceleration of the vehicle.
The principal object of the invention is to provide a control mechanism carried out as a shuttle orifice that facilitates long response times by providing a very small open cross-sectional area, that is self-cleaning, and that is fabricable in close tolerances and in a technological simple and inexpensive way.